1. Field of the Invention
The present invention relates to a liquid crystal display element superior in its viewing angle characteristic. Moreover, the present invention relates to a method including a process of performing a liquid crystal alignment treatment and a pre-tilt angle forming treatment by irradiating a polarized ultraviolet ray for manufacturing a liquid crystal display element superior in its viewing angle characteristic.
2. Description of the Related Art
In a mechanical rubbing method that is performed as a liquid crystal alignment treatment at the time of manufacturing a liquid crystal display element, there have been caused problems such as pollution by dust risen at the time of rubbing, electrostatic damage caused by friction to a transparent substrate on which a TFT (Thin Film Transistor) element is loaded, and the decline of the manufacturing yielding percentage owing to the pollution and the electrostatic damage.
Consequently, in place of the mechanical rubbing method, there is drawn attention a photo-alignment control technique capable of causing the liquid crystal alignment without touching. See Japanese Patent Application Publication Hei 07-318942 (basic application of U.S. Pat. No. 5,604,615), etc.
This technique is a technique for realizing directionality and a pre-tilt angle of the liquid crystal alignment in an organic alignment film formed on a transparent substrate by causing a chemical change of molecules composing the organic alignment film in accordance with the polarized direction of an ultraviolet ray irradiating the organic alignment film. Consequently, the technique can prevent occurrence of the pollution owing to the dust risen at the time of the mechanical rubbing and the electrostatic damage to the board on which the TFT element is loaded, and can prevent the decline of the manufacturing yielding percentage.
Furthermore, because the technique can make the polarized ultraviolet ray irradiate only fine areas, the liquid crystal alignment of the fine areas in the liquid alignment film can easily be done. Therefore, the improvement in a visual field angle can be made by performing division alignments of one liquid crystal alignment film. To adduce an actual example, for making main viewing angle directions of a liquid crystal display element even in the vertical direction and the horizontal direction, the technique executes a liquid crystal alignment treatment of irradiating liquid crystal alignment films of upper and lower boards in four respective divided areas xe2x80x9caaxe2x80x9d, xe2x80x9cbbxe2x80x9d, xe2x80x9cccxe2x80x9d and xe2x80x9cddxe2x80x9d of one dot 70, shown in FIG. 7, with a polarized ultraviolet ray so that the liquid crystal alignments of the lower substrate become the directions of the dotted line arrow heads and so that the liquid crystal alignments of the upper substrate become the full line arrow heads. Because main viewing angle directions of respective divided areas become the directions of the stars in the figure as the results, the main viewing angle direction of the whole liquid crystal display element becomes a mixture of viewing angle characteristics in four directions of the up, the down, the right and the left. Consequently, an inversion phenomenon and the decline of contrast can be suppressed, so that the visual field angle becomes good.
Incidentally, in this case, for using the main viewing angle directions of the liquid crystal display element of two directions of the right and the left, it is applicable to divide one dot into two areas.
However, in a case where the liquid crystal alignments are executed by diving one dot into two or four areas like the prior art technique, because alignment disorder occurs at boundaries of the divided areas (division boundaries), it is necessary to shade the upper substrate where a color filter is formed from rays penetrating the divided areas. For this reason, it is necessary to dispose shading areas at not only between dots but also crossing areas in a dot as denoted by the reference numerals 70a and 70b in FIG. 7. Consequently, a decline of aperture ratio of a dot and a decline of the transmissivities of rays are caused, and thereby there is caused a problem that the display quality of the liquid crystal display element declines as a result. The tendency becomes remarkable as the dot becomes finer, and the manufacturing yielding percentage also becomes declined.
Furthermore, when manufacturing such a liquid crystal display element, the liquid crystal alignment is performed by the irradiation of the polarized ultraviolet ray in conformity with the technique. But, the technique has problems such that it is difficult for the technique to define the alignment direction of a liquid crystal strictly and also it is difficult for the technique to develop a prescribed pre-tilt angle stably in comparison with the mechanical rubbing method. Consequently, problems of declinations of display quality such as the occurrence of unevenness of alignment and a declination of transmissivity and contrast of a display using a liquid crystal cell the liquid crystal alignment treatment of which has been performed by irradiating a polarized ultraviolet ray thereon are not resolved yet. That has been a great barrier to perform the mass production thereof.
The present invention aims to resolve the aforesaid problems of the prior art, and aims to provide a liquid crystal display element having a superior viewing angle characteristic without causing a decline of aperture ratio and a decline of transmissivity of a ray at a pixel composed of a group of three dots of an R-dot, a G-dot and a B-dot, or each dot. Moreover, the present invention also aims to realize a good liquid crystal alignment direction and a stable and even pre-tilt angle by means of a polarized ultraviolet ray without a decline of the manufacturing yielding percentage at the time of manufacturing such a liquid crystal display element.
The inventor of the present invention found the following facts and has completed a liquid crystal display element of the present invention. That is, the main viewing angle direction of the whole liquid crystal display element can be adjusted in an intended direction by performing a division alignment treatment of a liquid crystal alignment film on a transparent substrate while keeping a unique alignment direction at each pixel not dividing a pixel (ordinary composed of a group of an R-dot, a G-dot and a B-dot) and differentiating alignment directions at least between two pixels so as to be able to obtain an intended main viewing angle direction. And further, if a dot is still finer, the superior viewing angle characteristic can be obtained by performing the adjustment of the main viewing angle direction by the dot, not by performing the control of the main viewing angle by the pixel.
Furthermore, the inventor of the present invention found the following fact and has completed a method for manufacturing a liquid crystal display element of the present invention. That is, it is possible to develop a superior viewing angle characteristic and an even and stable liquid crystal alignment and pre-tilt angle of the liquid crystal display element without a decline of the manufacturing yielding percentage by irradiating a liquid crystal alignment film on a transparent substrate by the pixel and/or by the dot with divided polarized ultraviolet rays in a manner that the irradiation of the polarized ultraviolet ray is first performed for regulating liquid crystal alignment directions, and that the transparent substrate is next rotated, and further that the divisional irradiation of the polarized ultraviolet ray is again performed by the pixel or by the dot for regulating the pre-tilt angle of the liquid crystal.
That is to say, according to a first aspect of the present invention, there is provided a liquid crystal display element including a pair of transparent substrates, a liquid crystal sandwiched between the pair of transparent substrates, and liquid crystal alignment films formed on liquid crystal side surfaces of the respective transparent substrates, wherein the liquid crystal alignment films are aligned dividedly by a dot and/or by a pixel, and liquid crystal alignment directions at two dots or more and/or at two pixels or more differ from each other so that it is possible to obtain an intended main viewing angle direction.
It is needless to say that the division by the dot and the division by the pixel may be intermingled by performing a division alignment composed of alignments by the dot in some areas of the liquid crystal display element and alignments by the pixel in the other areas of the liquid crystal display element.
Furthermore, according to a second aspect of the present invention, there is provided a method for manufacturing a liquid crystal display element including a pair of transparent substrates, a liquid crystal sandwiched between the pair of transparent substrates, and liquid crystal alignment films formed on liquid crystal side surfaces of the respective transparent substrates, the method comprising the steps of (a) forming ultraviolet ray responsive type liquid crystal alignment films on the pair of transparent substrates, (b) irradiating the liquid crystal alignment films on the transparent substrates parallel to a reference plane with a polarized ultraviolet ray dividedly by a dot and/or by a pixel so that liquid crystal alignment directions at two dots or more and/or at two pixels or more differ from each other for obtaining an intended main viewing angle direction so as to regulate an alignment direction of the liquid crystal, and (c) irradiating the transparent substrate, on which the liquid crystal alignment films irradiated with the polarized ultraviolet ray at the step (b) are formed, with the polarized ultraviolet ray dividedly by the pixel for developing a pre-tilt angle after rotating the transparent substrate on the reference plane so that the transparent substrate turns to a direction different from its direction in the step (b).
It is needless to say that the division by the pixel and the division by the dot may be intermingled in a liquid crystal display element also in this case.
According to the aforementioned aspects of the present invention, a liquid crystal display element is manufactured by irradiating divided area thereof by the pixel and/or by the dot with a polarized ultraviolet ray without using the conventional mechanical rubbing method. Consequently, the manufactured liquid crystal display element exhibits a superior viewing angle characteristic without a decline of its aperture ratio, a decline of its transmissivity of rays and a decline of its manufacturing yielding percentage. Moreover, because the division irradiation of the polarized ultraviolet ray is performed at predetermined two steps, good alignment directions and a stable and uniform pre-tilt angle of liquid crystal molecules can be realized. Consequently, an electro-optical characteristic of the manufactured liquid crystal display element becomes good.